Equivalent of "rsync --delete"

I recently migrated from a NV+ to a RN 214. Firmware is 6.8.0. I have 4 33TB disks, and also 2 USB disks attached (3TB+2TB) for backups.

In addition I have another Linux server with a 3TB USB disk attached.

One share is backed up to the remote server using rsync, and for that, with the "advanced" tab I can "Remove deleted files on target" (like rsync --delete) so that the backup is an exact copy of the RN share. That is fine.

But for the backups to locally attached USB disks, this option isn't available ("Advanced options are available only for Rsync jobs"). So the backup is going to accumulate a lot of cruft over time.

I found out that I can do a "remote" backup using rsync via ssh from "nas" to "nas" to get the desired effect. But is there an easier way to get a local backup to add the "--delete" option?

Thanks -- Peter